For Quetelet, the bell curve represented accidental deviations from a sort of Platonic ideal he called l’homme moyen—the average man. When Galton stumbled upon Quetelet’s work, however, he exultantly saw the bell curve in a new light: what it described were not accidents to be overlooked but differences that reveal the variability on which evolution depends. His quest to find the laws that governed how these differences were transmitted from one generation to the next led to what has been justly deemed Galton’s greatest gifts to science: regression and correlation.
